Acid-mediated transformation of spirocyclopropyl oxetanes: a facile approach to spirocyclopropyl butenolides and γ-butyrolactones

Spirocyclic oxetanes were found to undergo versatile transformations under different acid-mediated conditions. Treatment of spirocyclopropyl oxetanes with excess amounts of hydrochloric or hydrobromic acid at room temperature resulted in the formation of spirocyclopropyl fused butenolides with good yields. The transformation of spirocyclopropyl oxetanes mediated by hydroiodic acid led to spirocyclopropyl fused gamma -butyrolactones instead of butenolides. Transformation of spirocyclopropyl oxetanes catalyzed by Lewis acid was also explored and found to give distinct products such as spirobutyl indolinones. The reaction mechanisms involved in the acid-mediated transformations were proposed.